The seroprevalence of HIV antibodies in surveyed intravenous substance users (IVSUs) who were either recently enrolled into treatment or were on a waiting list for enrollment was 29%. The rate among ARC research subjects with parenteral drug use histories has averaged 24%, and among area prostitutes with heavy drug use histories, 34%. In Baltimore, 94% of IVSUs had shared needles, and even though HIV seropositivity was not assoicated with a needle-sharing history, there was an association between the intensity of sharing and the probability of being seropositive. A much stronger association was observed between seropositivity and "shooting gallery" visitation, suggesting that this milieu of sharing, rather than other environments, is the real risk factor. Very distinct ethnic group differences in HIV infection were observed, with Blacks being much more likely to be seropositive than Whites (odds ratio = 8.18, 95% CI 3.35-19.97). There was no significant difference in HIV infection between Blacks in Baltimore and in New York City. Shooting gallery visitation appears to be much more a phenomenon among Black IVSUs than it is in White (X2 = 8.23, p<0.01). HIV infection has appreciably penetrated Baltimore's addict community. The overall seroprevalence rate in Baltimore in 1986 (29%) approximated that of New York in 1979 (27%) where the rate subsequently jumped to 58% in some areas by 1984 and has increased to 60% in 1987. Hepatitis antigen and antibody status of these subjects has been assessed. There was no concordance of Hepatitis B infection and HIV infection. Other data concerning Hetatitis D is being analysed. The second wave of this study is being initiated.